Most agricultural vehicles rely on substantial air cooling for their engines, drives, even air-conditioning systems. Since, however, these vehicles typically work in fairly dusty and dirty circumstances, it is necessary to filter the air before running it over or through the various heat exchangers the vehicle might have.
Accordingly it is standard practice to form the air-intake filter as a perforated drum centered on an axis and having an axially directed perforated end and a radially directed perforated side. The drum is rotated about its axis and a cleaning device is provided which covers a pie-shaped segment of the drum, so that each time the drum rotates it passes through the cleaner and in theory any particles on outer faces of the drum are removed.
European 0,269,765 describes a cleaning device that has a pressure tube whose rear end is in the air stream downstream of the fan and upstream of the cooler so that there is constantly air flow back through it. Directly behind its end the tube is bent through 180.degree. and extends with its upwardly open part along the outer surface of the rotating coolant filter. In another embodiment the pressure tube lies with its open part at a slight spacing in front of the outer end face of the rotating coolant filter. In both cases the thus channeled air flow of the tube blows particles out of the holes of the rotating coolant filter, or at least blows out those particles that are fairly light and are not lodged in place. Since the air flow only runs along the described surface region it cannot free particles stuck on the outer surface of the coolant filter or particles lodged in its holes. In addition the air current is not very effective since the air intake end of the tube has a very small flow cross section and the various deviations from a straight path cause a considerable loss of static pressure.
Another variant is known from German 195 46 321 wherein the rotating coolant filter is mounted on a stationary tube whose one end is closed. Its open ends holds a pressure tube that again engages with its bent-over end in the air stream downstream of the heat exchanger or the fan. In the region inside the coolant filter the tube, which carries the filter, is formed on its lower side with a hole on which an downwardly open outlet is connected that extends close to the surface and reaches over a portion of the end of the rotating filter. Underneath the outlet is a separating passage for leading off the dislodged particles of crop and dirt. The disadvantage of this solution is once again the limited effectiveness of the feeble air flow since the flow cross section of the bent end of the tube is too small and the tube's path is to circuitous. Although blow cleaning of the filter is basically preferable to a surface blowing-away as in the system of above-mentioned EP 0,269,765, the overall cleaning capacity of this system is unacceptable.
A system working in principle the same way is seen in German 40 33 204 and 195 47 348. It only differs in the suction fan used. Here a housing is set from outside on the end and side of the coolant filter that is at least partially open on its side directly juxtaposed with the filter. The surface of the filter covered by this housing is only a small fraction of its overall surface area so that it does not significantly reduce air flow through the filter. This housing is connected to the intake of a separate fan via a flexible tube so as to vacuum particles off the outside face of the filter and expel them remotely. Inside the filter directly across from this housing is a shield in the shape of a planar plate that prevents air from flowing through the filter at this location so that the suction of the particle fan is not working against the suction of the coolant fan. Such a device is not highly effective in removing particles adhered to the outer filter face or lodged in its openings.
Another system described in German 44 04 401 has a shield formed as an inner housing that is open toward the inner face of the filter. The thus formed opening of the inner housing is substantially larger than that of the outer housing that is connected to the intake of the particle fan so that some air flow through the filter is possible, in a direction that is the reverse of the direction of the cooling air. The disadvantage of this system is that air is sucked in the normal direction through the filter into the inner housing and then reversed and sucked out, so that this flow can effectively lodge particles in the holes so they cannot be dislodged by simple air flow. As in the other above-described systems, the filter therefore require periodic manual cleaning.